Research by Eshani Hettiarachchi, a PhD candidate studying with Gayan Rubasinghege in the New Mexico Tech Chemistry Department, and Shaylene Paul, who was an intern at the Bureau of Geology while a student at Navajo Technical University.This research is one of several Energize New MexicoEPSCoR projects focusing on uranium mineralization and mine-site remediation.
Many metals can be harmful to humans when they are taken into the body. We often think of drinking water when we think of these sources, however, toxic metals can also be taken into the body as inhaled particles or as part of our food. In this study, dust particles were mixed with one of two simulated lung fluids in an airtight glass reactor (configured as the figure to the right) where the solution was heated to a constant temperature of the standard human body temperatures – 37°C (98.6 °F) – in a vessel purged with oxygen just before adding the dust sample. The study found that the uranum in some dust samples (and lab standards) dissolved better in one or the other of the fluids and that this phenomenon seemed to be based on the mineralogy and available surface area of the dust and the pH of the fluid.
The two solutions simulated fluids from two different functional areas of the lungs and have significantly different chemistry and resulting pH: 1) the interstitial fluids that surround the cells within the lungs (pH 7.3); and 2) the fluids within macrophage cells, a type of white blood cell (pH 4.5). The cartoon image to the right demonstrates the fluid location in the body.
Using the XRD (X-ray Diffraction) instrument at the Bureau of Geology, the minerology of the dust samples was determined. The table below shows the mineralogy of dust samples from Jackpile Mine in Laguna Pueblo, NM (Sites A, C, E and G), and St. Athony Mine north of the Pueblo. The samples that contributed more uranium to fluid 1 (the interstitial fluid) are colored in green. The other samples contributed more uranium to fluid 2 (the macrophage fluid). One major different between the two sets of samples is the presence or absence of kaolinite or calcite. Samples with uranium that dissolved more readily to the interstitial fluid lacked kaolinite but contained calcite and carnotite. Sample uranium that dissolved more readily to the macrophage fluid lacked calcite and carnotite, but contained kaolinite. Further geochemical modeling also confirmed that uranium leaching from dust was dependent on mineralogy.
This project resulted in an article in the American Chemical Society journal (listed below) and is continuing with a study by Milton Das, another Chemistry PhD student, who is using simulated gastric and intestinal fluids to determine uranium dissolution from dust of larger particle sizes.
References
- Hettiarachchi, Eshani; Paul, Shaylene; Cadol, Daniel; Frey, Bonnie; and Gayan Rubasinghege, 2019, Mineralogy Controlled Dissolution of Uranium from Airborne Dust in Simulated Lung Fluids (SLFs) and Possible Health Implications. Environmental Science & Technology Letters: ACS Publications, Vol. 6, No. 2, p. 62-67, https://pubs.acs.org/doi/full/10.1021/acs.estlett.8b00557.